Baroclinic instability of ultra-long waves (wave numbers 1, 2, and 3) is studied with a 40-layer, geostrophic, hydrostatic, adiabatic model which is later modified to include Newtonian heating. The assumption of a meridionally-varying zonal current linear in pressure upon which are superimposed localized wavelike perturbations traveling in the west-east direction and static stability dependent only upon the inverse of pressure allows the reduction of the basic equations to a single second-order homogeneous ordinary differential equation in vertical pressure velocity having latitude as an implicit parameter. The “shooting method”, a numerical search procedure to determine the eigenvalue, perturbation phase velocity, is employed under the simplifying boundary conditions that vertical pressure velocity is zero at the top and bottom of the atmosphere. This method requires one exact solution, and a procedure is given to determine it. The adiabatic and Newtonian models are each solved for a zonal wind profile based upon the annual average, 1963 500 mb zonal wind from 25° N to 80° N. It is found that perturbation instability, which is decreased by Newtonian heating, is maximum at 35° N which, in the adiabatic model, corresponds to an e-folding time for the third harmonic of six days. Here, the phase speed, equivalent for adiabatic and Newtonian flow and independent of wave number, is 6 m sec?1. Near equivalence between the models is observed in the vertical structure, the waves tilting westward with decreasing pressure. Instantaneous energetics of the adiabatic and Newtonian models is studied by calculation of the vertical variation and total in a latitudinal strip 10° wide centered on the latitude of maximum instability of the normalized conversion from zonal to eddy available potential energy, C ( A z , A E ), and normalized conversion from eddy available potential energy to eddy kinetic energy, C ( A E , K E ). Here it is found, after summing over all pressures, that C ( A z , A E > 0 and C ( A E , K E ) > 0 for both models which agrees with the time-averaged energetics as observed in the atmosphere. DOI: 10.1111/j.2153-3490.1971.tb00573.x